Exchange time

In molecular mechanics and molecular dynamics studies of proteins, assig-ment of standard, non-dynamical ionization states of protein titratable groups is a common practice. This assumption seems to be well justified because proton exchange times between protein and solution usually far exceed the time range of the MD simulations. We investigated to what extent the assumed protonation state of a protein influences its molecular dynamics trajectory, and how often our titration algorithm predicted ionization states identical to those imposed on the groups, when applied to a set of structures derived from a molecular dynamics trajectory [34]. As a model we took the bovine... 

Craig, H. (1957b). The natural distribution of radiocarbon and the exchange time of carbon dioxide between atmosphere and sea. Tellus 9,1-17. 

Figure 1.17 Normalized temperature rise for a first-order exothermic reaction as a function of the ratio of reaction and heat-exchange time-scale, obtained from [114], Different activation temperatures are considered.

Comparison between xf a as determined on the basis of Eq. (3.1.15) from the microscopically determined crystallite radius and the intracrystalline diffusivity measured by PFG NMR for sufficiently short observation times t (top left of Figure 3.1.1), with the actual exchange time xintra resulting from the NMR tracer desorption technique, provides a simple means for quantifying possible surface barriers. In the case of coinciding values, any substantial influence of the surface barriers can be excluded. Any enhancement of xintra in comparison with x a, on the other side, may be considered as a quantitative measure of the surface barriers. 

Shell and tube heat exchangers Time base mid 2004... 

Figure 6.3a, b. Shell and tube heat exchangers. Time base mid-2004 Purchased cost = (bare cost from figure) x Type factor x Pressure factor... 

Figure 6.4a, b. Gasketed plate and frame and double pipe heat exchangers, Time base mid-2004... 

Figures 19.6, 19.7, and 19.9 provide results of steady-state water-gas shift in the absence of co-fed hydrogen. In Figure 19.6, the reactive exchange rates of formate and C02 were faster for the 1% Pt/Zr02 catalyst at 225°C (time to achieve 50% 13C incorporation, 3.5 min) than for the 2% Pt/Zr02 ( 5.7 min), as shown in Figure 19.7. Replacing N2 with H2 did not measurably impact the exchange time (Figure 19.8).

Fig. n.4 PLIMSTEX curve for 1.5 pM Ras-GDP titrating with Mg +. Conditions 90% D2O, 50 mM HEPES buffer, 100 mM KCI, pH 7.4, H/D exchange time = 3 h. EDTA was used to control [Mg +] in solution. The error bars shown for each data point were based on the deviation from two independent runs. 

To initiate an H/D exchange reaction, a protein sample, initially in non-deuterated buffer, is incubated in a buffer with 50-90% mole fraction deuterated water. There are almost no restrictions on reaction conditions which allow exchange behavior to be studied as a function of protein and buffer composition, solution pH, and in the presence and absence of ligands. To follow the deuterium buildup of individual amide hydrogen or sets of hydrogens, several on exchange time points are sampled for each condition. 

Ferritin The first correlation time is larger at 5°C (1.95 ns) than at 37°C (0.72 ns), as would be a rotational correlation time, a diffusion time or an exchange time. Nevertheless, neither the rotation time (0.19 ps at 37°C) nor the diffusion time (12.8 ns at 37°C) corresponds to this value. The first dispersion was therefore interpreted as arising from a proton exchange. The correlation time of the second dispersion (23 ns at 37° C) also decreases with temperature, and is about 8 times shorter than the rotation time. Nevertheless, it is closer to the value of the diffusion time. The second dispersion was therefore assigned to proton exchange or diffusion. 

Akaganeite particles Both Ti and T2 are strongly pH-dependent (Pigs. 17 and 19). The amplitudes of the longitudinal NMRD profiles drastically decrease when the pH increases from 3.35 to 9.45. The correlation time associated with the first dispersion is only weakly pH dependent, consistent with its former interpretation as an electron relaxation time. However, T2, the correlation time characteristic of the second dispersion, increases from 30 8 ns at pH 3.35 to 280 32 ns at pH 9.45, which eliminates its interpretation as a diffusion time T2 can be identified as a proton exchange time. 

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